Currently, there has been widespread RF (Radio Frequency) systems that communicate between a reader-writer device and an RF module in a non-contact form, and in which the reader-writer device and the RF module transmit information to each other. As the RF module, for example, a card-type RF module has been widespread, which is used for a variety of applications such as an electronic money, a commutation pass, and an employee ID card. As the RF system, for example, a near field communication (NFC) has been widespread, which is one of radio communication standards. NFC has recently been expected to be mounted in a variety of mobile devices including a mobile phone terminal. A radio signal in a 13-MHz band (HF band) is in use in NFC.
Each of the reader-writer device and the RF module includes an antenna that transmits and receives the radio signal, and an RFIC element that is connected with the antenna and processes the radio signal. In this configuration, the reader-writer device and the RF module transmit and receive predetermined information between the antenna of the RF module and the antenna of the reader-writer device through one of a magnetic field and an electromagnetic field. Thus, by the RF module approaching the reader-writer device (master unit), the reader-writer device can read and rewrite information stored in the RF module.
Patent Document 1 (identified below) discloses an RFID (Radio Frequency Identification) tag as the RF module. By the RFID tag approaching the reader-writer device (master unit), the reader-writer device can read and rewrite information stored in the RFID tag.
Patent Document 1: Japanese Patent No. 5010405.
However, in the conventional RF module, just by the RF module approaching the reader-writer device (master unit), important information may be transmitted from the RF module to the reader unit. The important information is, for example, personal information of a user who owns the RF module, a card number of the user, a validity date of the card, and the like.
Thus, just by bringing the RF module of the user close to the reader-writer device (communication device), a malicious person can steal the personal information of the user or settle card transaction without permission.